A base station apparatus (hereinafter, sometimes called as “array-antenna base-station apparatus”) using an adaptive array-antenna (hereinafter, sometimes called as “AAA”) comprises a plurality of antennas elements, and freely set the directivity by adjusting the amplitude and the phases of signals received with each antenna element. The directivity is formed by multiplication of received signals or transmitting signals by complex coefficients (hereinafter, the complex coefficient is called as “weight”).
The array-antenna base-station apparatus may intensely receive only signals from a desired direction by adjusting the above weights to be multiplied. This is called as “have adjustable received-directivity”. The array-antenna base-station apparatus may keep the received SIRs (Signal to Interference Ratios) of signals arriving from each direction high by having the received directivity so that a desired signal is received in an optimum manner.
On the other hand, a micro-cell method, in which a range (cell) to be covered by one base station is reduced, has been noticed in a mobile communication field from a viewpoint of reuse of frequencies. As the number of radio base stations necessary for serving the same area is increased in the above micro-cell method, there have been problems that there are limitations on the installation space, weight, size and so on, and handover is frequently generated.
A radio base station apparatus in which a relay-station apparatus and a control-station apparatus are connected using metallic cables has bee proposed as means for solving the above problems. The above radio base station apparatus has a configuration where a control-station apparatus, which mainly comprises a radio modem section and a control section in a conventional base section, is centralized and arranged in the center, and a large number of relay-station apparatuses, which mainly comprise antennas and transmitting and receiving amplifiers, are provided. Thereby, the above limitation on the installation space may be eliminated, as the above base station may be made smaller and lighter. Moreover, the handover processing may be also performed with the above control-station apparatus in a centralized manner.
FIG. 1 is a block diagram showing a configuration of a conventional array-antenna base-station apparatus using metallic cables for connecting the above control-station apparatus and the above relay-station apparatus. Here, only the receiving side of the array-antenna base-station apparatus is shown for brief description. In addition, only one relay-station apparatus is shown in the drawing for brief description, though the control-station apparatus is generally connected to a large number of relay-station apparatuses.
As shown in the drawing, a relay-station apparatus 11 has a configuration comprising: antennas 12-1 through 12-N; and receiving amplifiers 13-1 through 13-N. A control-station apparatus 21 has a configuration comprising; frequency conversion sections 22-1 through 22-N; and a demodulating section 23. The above relay-station apparatus 11 and control-station apparatus 21 are connected through metallic cables 31-1 through 31-N.
As the same manner is used for processing of any received signals on N different paths corresponding to each of the above antennas 12-1 through 12-N, processing on only the path corresponding to the antennas 12-1 will be described below.
In the relay-station apparatus 11, the above receiving amplifier 13-1 amplifies received signals which are received from a communication terminal apparatus (not shown) of a communication end through the antenna 12-1, and outputs the amplified signals to the above frequency conversion section 22-1 through the metallic cable 31-1. In the control-station apparatus 21, the frequency conversion section 22-1 converts the frequency of the received signals from the receiving amplifier 13-1 from a radio frequency band to a baseband frequency one for output to the demodulating section 23. The above demodulating section 23 demodulates received signals (baseband signals) output from the frequency conversion sections 22-1 through 22-N by multiplication of the above signals by weights.
Then, processing of received signals taken into the base station apparatus with the above configuration will be described.
Received signals, which have been taken into the relay-station apparatus 11 through the antenna 12-1, from a communication terminal apparatus (not shown) are sent to the control-station apparatus 21 through the metallic cable 31-1. The received signals sent to the control-station apparatus 21 are amplified in the frequency conversion section 22-1, and thereafter, demodulated in the demodulating section 23 after multiplication by weights. Thus, the received SIRs may be kept high in the array-antenna base-station as the above array-antenna base-station may intensely receive signals from a specified direction by multiplication of the received signals by weights.
However, the above conventional array-antenna base-station apparatus has had the following problems:
1) Loss in transmitted signals is large, as metallic cables are used for signal transmission from the relay-station apparatus to the control-station apparatus.
2) There are limitations on the installation space, as it is required to transmit signals taken in from a plurality of antenna elements, and larger number of metallic cables are increased.
3) The signals received through each antenna element reaches the demodulating section 23, passing through a path corresponding to each antenna element. The characteristics of the above paths depend on the differences of the characteristics between analog devices provided in amplifiers, and so on. Accordingly, the directivity obtained in the demodulating section deviates from the desired one due to unknown amplitude fluctuations and the phase rotations added to each received signal. Though the characteristics of each path may be previously measured at installation for adjusting the deviations, it is difficult to maintain the desired directivity for a long time, as the above characteristics of each path changes with the passage of time according to the changes in the temperature and so on.